Fluororubbers are excellent in such characteristics as chemical resistance, solvent resistance and heat resistance and, therefore, they are widely used as sealants or like materials which can be used under severe conditions.
Known in the art is a curable fluoropolyether rubber composition containing a linear fluoropolyether compound having at least two alkenyl groups in each molecule and having a perfluoropolyether structure in the main chain thereof (cf. e.g. Japanese Kokai Publication 2001-354764). However, since the polymer in this composition has a main chain with a perfluoro structure, there arise problems; namely, the composition is poor in compatibility with materials or compounds other than perfluoro compounds and difficult to adhere to other materials or mix with other formulating ingredients or additives. Another problem is that an expensive dicarboxylic acid compound is required in synthesizing the polymer.
Also known is a curable composition comprising a fluorine-containing oligomer having an unsaturated group at each terminus of the main chain thereof and having a number average molecular weight of 1,000 to 10,000 and a (meth)acrylic monomer, together with a photopolymerization initiator or radical generator (cf. e.g. Japanese Kokai Publication 2001-81131). However, this composition has problems; namely, a UV irradiation apparatus is required for curing this curable composition using a photopolymerization initiator and, in the curing reaction of the curable composition using a radical generator, byproducts causing foaming are generated.
Therefore, a mixture comprising a lateral double bond-containing fluoroelastomer resulting from polymerization of a small amount of a monomer containing at least two olefinic double bond, for example triallyl isocyanurate, and an Si—H group-containing silicone elastomer and so forth, together with a specific catalyst, and which is to be cured by the hydrosilylation reaction has been proposed (cf. e.g. Japanese Kokai Publication H06-192524).
However, the cured material obtained from this mixture has problems about mechanical strength and other characteristics. Further, there is no disclosure or suggestion about the effect and so forth in connection with this fluoroelastomer having an olefinic double bond at a chain terminus.